The goal of this work is to understand the role of membrane lipids in a number of membrane changes associated with malignant transformation of chick embryo fibroblasts by Rous sarcoma virus. The membrane changes which will be studied in most detail are alterations in transport of molecules across the cell membrane, changes in adenyl cyclase activity and morphogenesis of Rous sarcoma virus at the cell membrane. The roles of fatty acids, cholesterol and phospholipids will be assessed primarily by providing these lipids as supplements to normal and transformed cells, thus modifying the cells' lipid composition, and analyzing the effects of these supplementations on the transformed phenotype and virus morphogenesis. The effects of the supplementations on the biophysical properties of the membrane bilayer will be assessed using fluorescence and electron spin resonance techniques. These analyses will be complemented by the use of mutants of Rous sarcoma virus which are temperature-conditioned either for transformation or morphogenesis.